Journal: Transactions of IAA RAS vol. 40
Keywords: VLBI, Astrometry
Minute motions of the cores of radio quasars and BL Lac objects and the chromatic dependence of the positions of those cores (the so-called core shift) can be studied by means of VLBI phase delay astrometry. We report on the results of 14.4/43.1GHz VLBA observations of the complete S5 polar cap sample carried out in 2010 compared to 15 GHz observations made in 2000. The successful 43 GHz observations in 2010, globally phase-delay connected for the first time, mark the state-of-the-art of the technique and probably its limit.